PEDIATRIC MEDULLOBLASTOMA - RADIATION TREATMENT TECHNIQUE AND PATTERNS OF FAILURE

Purpose: In this study factors are analyzed that may potentially influ ence the site of failure in pediatric medulloblastoma. Patient-related , disease-related, and treatment-related variables are analyzed with a special focus on radiotherapy time-dose and technical factors. Method s and Materials: Eighty-six children and adolescents with a diagnosis of medulloblastoma were treated in Switzerland during the period 1972- 1991. Postoperative megavoltage radiotherapy was delivered to all pati ents. Simulation and portal films of the whole-brain irradiation (WBI) fields were retrospectively reviewed in 77 patients. The distance fro m the field margin to the cribiform plate and to the door of the tempo ral fossa was carefully assessed and correlated with supratentorial fa ilure-free survival. In 19 children the spine was treated with high-en ergy electron beams, the remainder with megavoltage photons. Simulatio n and port films of the posterior fossa fields were also reviewed in 7 2 patients. The field size and the field limits were evaluated and cor related with posterior fossa failure-free survival. Results: In 36 pat ients (47%) the WBI margins were judged to miss the inferior portion o f the frontal and temporal lobes. Twelve patients failed in the suprat entorial region and 9 of these patients belonged to the group of 36 ch ildren in whom the inferior portion of the brain had been underdosed. On multivariate analysis only field correctness was retained as being significantly correlated with supratentorial failure-free survival (p = 0.049). Neither the total dose to the spinal theca nor the treatment technique (electron vs. photon beams) were significantly correlated w ith outcome. Posterior fossa failure-free survival was not influenced by total dose, overall treatment time, field size, or field margin cor rectness. Overall survival was not influenced by any of the radiothera py-related technical factors. Conclusion: A correlation between WBI fi eld correctness and supratentorial failure-free survival was observed. Treatment protocols should be considered that limit supratentorial ir radiation mainly to subsites at highest risk of relapse. Optimized con formal therapy or proton beam therapy may help to reach this goal. Tre ating the spine with electron beams was not deletereous. A significant correlation between local control and other technical factors was not observed, including those relating to posterior fossa treatment. The use of small conformal tumor bed boost fields may be prefered to the l arger posterior fossa fields usually considered as the standard treatm ent approach. (C) 1997 Elsevier Science Inc.